1. Field of the Invention
The present invention relates to an optical waveguide filter, and more particularly, to an optical waveguide filter using a multi-mode interference.
2. Description of Related Art
As a data transmission capacity increases, a wavelength division multiplexing (WDM) system is recently in the spotlight. The WDM system requires a transceiver module that performs an optic-electric conversion and an electric-optic conversion. In particular, since the WDM system is a two-way communication system having a wavelength of 1310 nm and 1550 nm, a filtering element of the transceiver module is a very important element that separates the two wavelengths.
Such a filtering element includes a beam splitter, a directional coupler and a thin film filter.
The beam splitter (e.g., disclosed in Korean Patent Publication no. 2001-41551) relates to a two-way optical circulator and a wavelength divider module that can amplify an optical signal in both two ways in order to achieve a two-way optical communication through a single optical fiber.
However, the beam splitter has a disadvantage in that it is difficult to integrate the beam splitter and to configure the beam splitter together with a peripheral transmitting/receiving circuit.
The directional coupler (e.g., disclosed in Korean Patent Publication no. 1999-20073) is a waveguide element that makes two waveguides close to each other and changes a propagating path of an optical signal from one waveguide to the other waveguide using a mode-coupling refractive index.
The thin film filter (e.g., disclosed in Korean Patent Publication no. 2001-10582) is a wavelength filtering element that deposits a dielectric film having a suitable refractive index on a substrate to reflect or transmit a desired wavelength.
However, even though it is possible to integrate, the directional coupler and the thin film filter have a problem in that there is a limitation as to a miniaturization and a manufacturing tolerance is low.
To overcome the problems described above, preferred embodiments of the present invention provide an optical waveguide filter which is suitable for an integration and a miniaturization.
It is another object of the present invention to provide an optical waveguide filter having a large manufacturing tolerance.
It is a still object of the present invention to provide an optical waveguide filter which is relatively less sensitive to a TE/TM polarization in consideration of an optical loss.
It is a still yet object of the present invention to provide an optical waveguide filter which is low in loss resulting from a connection with peripheral elements.
It is still another object of the present invention to provide a small-sized optical waveguide filter.
In order to achieve the above object, the preferred embodiments of the present invention provide an optical waveguide filter using a multi-mode interference and having a predetermined width, a predetermined length and a predetermined thickness, comprising: a transmitting light source and a photo detector coupled to one side thereof; and a transmission line coupled to the other side thereof, wherein one hundred percent of an output optical power having a first wavelength from the transmitting light source is transferred to the transmission line, and one hundred percent of an input optical power having a second wavelength from the transmission line is transferred to the photo detector.
A length between the transmission line, and the photo detector and the transmitting line is determined by a beat length ratio. The transmitting light source and the photo detector are located at trisection points of the width of the filter. The transmission line is located at a trisection point of the width of the filter.
The present invention further provides an optical waveguide filter using a multi-mode interference and having a predetermined width and a predetermined length, comprising: a transmitting light source and a photo detector coupled to one side thereof; and a transmission line and a monitoring photo detector coupled to the other side thereof, wherein an output optical power having a first wavelength from the transmitting light source is divided at a predetermined percent and transferred to the transmission line and the monitoring photo detector, and one hundred percent of an input optical power having a second wavelength from the transmission line is transferred to the photo detector.
A length between the transmission line and the monitoring photo detector, and the photo detector and the transmitting line is determined by a beat length ratio. The transmitting light source and the photo detector are located at trisection points of the width of the filter, at quadrisection points of the width of the filer, or at points that the width of the waveguide is divided into five. The transmission line and the monitoring photo detector are located at trisection points of the width of the filter, at quadrisection points of the width of the filter, or at points that the width of the filter is divided into five.
The optical waveguide filter using a multi-mode interference according to the present invention has the following advantages. First, the optical waveguide filter anticipates an optical power distribution ratio. Also, since a length of the optical waveguide filter can be reduced compared to the conventional directional coupler, an integration and a miniaturization of the optical waveguide filter can be achieved. Further, since the optical waveguide filter has a width of tens of micrometers (xcexcm), the optical waveguide filter can have a large manufacturing tolerance. The inventive optical waveguide filter can be made insensitively to the TE/TM polarization even though an optical loss occurs. Besides, since the optical waveguide filter is small-sized and can be manufactured in a single manufacturing process, the optical waveguide filter is low in loss resulting from a connection with peripheral elements such as a laser diode or a photo detector.